Generally, any color "screen of death" on reboot (whether it rebooted spontaneously or you deliberately powered down/back up) is a pretty big sign of something going wrong in hardware. If it's only happened once, you're not stock in a bootloop, and you're not jailbroken, it may be nothing to worry about. (If you're jailbroken, there's a chance conflicting tweaks are triggering this behavior, so start by removing the most recent ones.)
But if it's happened multiple times or you're stuck in a bootloop, take it to Apple for exchange.